• advanced high strength steel;
  • microstructure;
  • quenching and partitioning

The recently developed “quenching and partitioning” (Q&P) and “quenching–partitioning–tempering” heat treatment are both novel processing technologies, which are aim to achieve advanced high strength steels with good combination of high strength and ductility. Containing certain amount of ductile austenite phase is a key characteristic of the Q&P steel, and austenite phase is being enriched with carbon during the partitioning treatment. However, the microstructural evolution of the Q&P steel during the heat treatment is rather complicated. In present work, evolution of microstructure in medium carbon steel containing Cr, Mo, and Nb has been studied in detail during the Q&P process. The microstructural evolution of the steel was investigated in terms of X-ray diffraction, scanning electron microscope, and transmission electron microscope.